In general, in manually feeding a robot for a teaching operation, an operator selects a feed rate by operating an override key on a console panel or the like, and then operates manual feed keys associated with the individual axes of the robot to operate the axes either individually or in an interlocked manner. As safety measures for reducing damage, which may occur by collision of the robots during the teaching operation, it is known in the art to restrict the upper limit of the override value selectable for an operator in the teaching mode within a preset acceptable range.
In the actual teaching operation, when there are no obstacles in the vicinity of the robot as an object of the teaching operation, the operator will set a large override value within an acceptable range, thereby operating the robot at a relatively high manual feed rate for efficient teaching operation. If there are any obstacles in the region of the robot as an object of the teaching operation and, if the robot is approaching the obstacles during the manual feed of the robot, the operator must set the override value to a smaller value to operate the robot at a relatively low manual feed rate, thereby securing a safety against collision.
Recently, however, it has become a common practice to closely arrange a multiplicity of robots for saving the working space and working time, which naturally necessitates the teaching operations of the individual robots in a state where a plurality of robots interfere with one another. In this case, for the robot as an object of the teaching operation, all other robots located around the robot can be obstacles. In particular, where a plurality of robots are to undergo teaching operations at a time, for example, in such a case where the teaching operation of a first robot is temporarily stopped and then resumed after finishing the teaching operation of a second robot, positional relationships between the first robot and other robots at the time when the teaching operation of the first robot is stopped temporarily may differ variously from positional relationships between the first robot and other robots at the time when resuming the teaching operation of the first robot. More specifically,in such a case, the distances may vary between the robot as an object of the teaching operation on and other robots as obstacles. Thus, if it is desired to advance the teaching operation effectively and safely, there must be a resetting of the override value of the robot as an object of the next teaching operation each time the position and posture of one robot is changed. This method, however, makes the resetting operation itself complicated and may result in a decrease of the working efficiency of the entire teaching operation.
On the other hand, if the selective override value is fixedly set at a low level, a teaching operation will be unable to be performed at a high speed even when there is an ample space around the robots. If a teaching operation is carried out with the override value selected for a high-speed feeding in disregard of the surrounding conditions, the robot will suffer great damage if an inadvertent collision occurs.